The invention is related to a method for producing optical glasses, in which the glasses are polished and marked following a shaping processing.
The invention, further, is related to an apparatus for producing optical glasses, in which the glasses are polished and marked following a shaping process.
A method and an apparatus of the type specified before are known from WO 01/66308 A1.
The invention will hereinafter be described with regard to an application for spectacle lenses. However, it goes without saying that the invention may also be applied for other optical glasses.
It is well known that so-called single-vision spectacle lenses are defined by two spherical surfaces or by one spherical and one toroidal surface. For optimising the central thickness and the peripheral thickness of single-vision spectacle lenses, a rotational symmetric aspherical function may be superimposed to the spherical or to the toroidal surface on one of the two sides of the lens.
In contrast, so-called progressive power lenses or multifocal lenses have at least one optical free-form surface computed by optimisation software. The free-form surface is not rotationally symmetrical. Conventionally, it is located on the front surface of the spectacle lens. The so-called prescription surface, in contrast, is located on the toroidal rear surface of the spectacle lens and is adjusted to the optical characteristics of the spectacle user.
Plastic material progressive power lenses are produced by molding. With this type of production, the optical free-form surface is generated already during the forming process. Spectacle lenses made from silicate, in contrast, are produced by an iterative sequence of processing steps of grinding and of polishing.
The toroidal prescription processing is executed by grinding and polishing machines as are well known in the prior art.
The prior art, further, comprises spectacle lenses, the optical characteristics of which are individually computed and optimised for any spectacle lens. Such prior art spectacle lenses, therefore, have at least one individually computed optical surface in a spline representation. The production of such individual optical surfaces is conventionally executed for non-rotationally symmetrical plastic material spectacle lenses by means of diamond lathing techniques. Such lathes are known from WO 97/13603 as well as from EP 0 758 571 B1. These prior art diamond lathes operate with an automatic feeding of the spectacle lenses in connection with a conveyor belt. The spectacle lenses are affixed to blocks and are transported in ordering boxes.
When plastic material progressive power lenses are processed on their surface by means of a diamond lathing technology, they show a regular surface groove structure after the completion of the lathing process. This structure is of the order of 80 to 200 nm rms surface roughness. For obtaining the necessary final roughness of less than 10 nm rms, these lathed optical surfaces must still be polished. Finally, a so-called signature has to be applied. The signature or labelling is understood to be a marking for product identification on the one hand. On the other hand the application of two markings on each spectacle lens may define the optical axis, thereby assisting the optometrist to fit a lens into the spectacle frame in their correct position.
As chips are generated during the polishing process, the polished surfaces must be cleaned from the chips and from the polishing agent and must be dried thereafter, prior to the subsequent marking step.
A polishing machine, as may be used in the above-described context, is described in WO 01/56740 A1.
In practice, for polishing lathed or ground free-form surfaces, polishing tools are used, in which a polishing surface is configured as a disposable polishing coating. The polishing surface is supported by an elastic foam structure such that the polishing surface may adapt itself to the shape of the spectacle lens. The polishing surface is shaped either convex or concave, depending on whether concave or convex spectacle lens surfaces shall be polished.
After each polishing process the worn disposable polishing coating is detached from the polishing tool and is replaced by a fresh polishing coating. Following the detachment of the worn polishing coating the polishing tool is cleaned and dried.
During the subsequent marking of the spectacle lenses the above-mentioned marking is conventionally applied into the spectacle lens surface pointwise, i.e. as a dot pattern, by means of a laser beam.
All of the afore-described prior art apparatuses for polishing, washing and marking have in common that the spectacle lenses are fed individually, mostly manually.
WO 02/00392 A1 describes an apparatus for loading and for unloading optical work pieces. This prior art apparatus is preferably used in connection with a grinding machine for optical single lenses. In this prior art apparatus, the spectacle lenses are handled by means of a suction head being applied to the optical surface of the spectacle lenses. Although it is likewise suggested to use a pneumatically operated three finger gripper, the latter shall, however, only be used for centering the spectacle lenses.
U.S. Pat. No. 6,247,999 B1 discloses a method of automatically exchanging polishing tools. In this prior art method a plurality of polishing tools is placed ready in a row on a magazine bank. A robot picks up one of the polishing tools and attaches same to a gimballed suspension for the polishing tool at the drive element of the polishing machine. After completion of the polishing process the robot, together with the polishing tool moves into a device in which two metal sheets are arranged inclined with respect to the horizontal plane and enclose between them a gap. The robot enters the polishing tool into the gap and strips same off there. The worn polishing tool now falls downwardly into the inclined chute configured by the device and finally arrives at a container.
EP 0 567 894 A1 discloses an apparatus for guiding a work piece or a tool during the processing of toroidal or of spherical surfaces of optical lenses on grinding or polishing machines.
In this prior art apparatus a roller bellows is located at the lower free end of a spindle, the bellows supporting a polishing disk. An air pressure may be generated within a volume enclosed by the roller bellows, such that the polishing disk may be displaced axially. Moreover, the polishing disk is supported by an axially acting piston via a spherical joint. The roller bellows is adapted to transmit a torque for the polishing disk when rotated during operation.
This prior art apparatus has the disadvantage that the roller bellows is a relatively stiff element such that the polishing disk may effect its proper movements only to a very limited extent.
EP 0 974 423 A1 discloses another similar polishing disk, wherein the polishing tool may be attached to an actuator element via a bayonet joint.
This prior art apparatus has the disadvantage that for attaching the polishing tool, the latter must be oriented in an angularly correct orientation relative to the actuator element.
Another similar apparatus is disclosed in EP 0 974 422 A1.